Ali Harzi was the only suspect in custody over the Sept. 11 attack on the consulate in Libya

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The only suspect in custody over the Sept. 11 attack on the U.S. consulate in Benghazi, Libya, has been released.

The only suspect in custody over the attack on the U.S. consulate in Benghazi has been conditionally released by Tunisian authorities due to lack of evidence.

An advisor to the Tunisian justice ministry confirmed to NBC News on Tuesday that Ali Harzi, a Tunisian, was released from custody by the investigative judge Monday but said that his release is temporary, he remains under investigation and he is subject to a travel ban.

Earlier, his lawyer Anwar Oued-Ali had said his client was freed Monday night but had to remain in the greater Tunis area in case the court needs him.

The release of Harzi represents a blow to the investigation of the Sept. 11 attack on the consulate in Libya that killed the U.S. ambassador and three other Americans. The investigation in Libya itself has been stalled due to the weak power of the central government in the face of the powerful militias, some of whom may have been involved in the attack.

Harzi had previously been interrogated by FBI officials in the presence of a Tunisian judge in December. He was originally detained in Turkey and in October was extradited to Tunisia, where authorities had said he was "strongly suspected" of being involved in the attack.

His lawyer had always maintained there was no evidence linking him to the attack.